Inks including segment copolymer grafted pigments via azide chemistry

ABSTRACT

Pigment based inks are provided. The inks include a non-polar carrier fluid; and a surface-functionalized pigment particle including a nitrogen-inked moiety to the surface of the pigment particle through a nitrogen link at one end of the nitrogen-linked moiety and a segment copolymer having at least two blocks attached at another end, the pigment particle suspended in the non-polar carrier fluid. A combination of an electronic display and an electronic ink employing the pigment and a process for making the pigment-based inks are also provided.

BACKGROUND

Ultrathin, flexible electronic displays that look like print on paperhave many potential applications including wearable computer screens,electronic paper, smart identity cards, store shelf labels, and signageapplications. Electrophoretic or electrokinetic displays are animportant approach to this type of medium. Electrophoretic actuationrelies on particles moving under the influence of an electric field.Accordingly, the desired particles must exhibit good dispersibility andcharge properties in non-polar dispersing media. Non-polar dispersingmedia are desirable because they help minimize the leakage currents inelectrophoretic or kinetic devices.

Current commercial products based on electrophoretic display technologyare only able to provide color and white states or black and whitestates. They cannot provide a clear or transparent state, which preventsuse of a stacked architecture design. A stacked architecture of layeredcolorants would allow the use of transparent to colored statetransitions in each layer of primary subtractive color resulting inprint-like color in one display.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of examples of the present disclosure willbecome apparent by reference to the following detailed description anddrawings, in which like reference numerals correspond to similar, thoughperhaps not identical, components. For the sake of brevity, referencenumerals or features having a previously described function may or maynot be described in connection with other drawings in which they appear.

FIG. 1 depicts a cross-sectional view of one example of a stackedelectro-optical display.

FIG. 2 illustrates a cross-sectional view of one example of a lateralelectro-optical display.

FIG. 3 is a schematic diagram of an example reaction scheme for forminga tetrafluorophenyl azide useful in the practice of the processesdisclosed herein.

FIG. 4 is a block diagram depicting an example process employed in thepractice of the present invention.

DETAILED DESCRIPTION

Reference is made now in detail to specific examples, which illustratesthe best mode presently contemplated by the inventors for practicing theinvention. Alternative examples are also briefly described asapplicable.

Reference is made now in detail to specific examples, which illustratesthe best mode presently contemplated by the inventors for practicing theinvention. Alternative examples are also briefly described asapplicable.

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific examples in which the disclosure may bepracticed. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of examples can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother examples may be utilized and structural or logical changes may bemade without departing from the scope of the present disclosure. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present disclosure is defined bythe appended claims.

As used herein, the term “grayscale” applies to both black and whiteimages and monochromatic color images. Grayscale refers to an imageincluding different shades of a single color produced by controlling thedensity of the single color within a given area of a display.

As used herein, the term “over” is not limited to any particularorientation and can include above, below, next to, adjacent to, and/oron. In addition, the term “over” can encompass intervening componentsbetween a first component and a second component where the firstcomponent is “over” the second component.

As used herein, the term “adjacent” is not limited to any particularorientation and can include above, below, next to, and/or on. Inaddition, the term “adjacent” can encompass intervening componentsbetween a first component and a second component where the firstcomponent is “adjacent” to the second component.

As used herein, the term “electronic ink display” is a display thatforms visible images using one or more of electrophoresis,electroconvection, electro-osmosis, electrochemical interactions, and/orother electrokinetic phenomena.

As used herein, “about” means a ±10% variance caused by, for example,variations in manufacturing processes.

The article ‘a’ and ‘an’ as used in the claims herein means one or more.

Significant progress has been made towards developing working electronicinks based on the electrokinetic mechanism using conventionalstabilization techniques and materials. However, improvements inreliability are still needed for commercially successful applications.These previous electronic inks are based on pigments with additionalsurfactants and charge directors, in which both charging andstabilization related functionality are not covalently bonded to thepigment surface. In this case, the pigment can lose charge with timeunder electric field or repeated switching cycles. The adsorbedstabilizing polymer material on the pigment surface is capable ofdesorbing and the free polymeric species in the solvent are capable ofdegradation as a result of cell operation. Additional surfactants in thesolvent also result in higher background charges which can lead to fieldscreening effects.

Surface modification of TiO₂ pigment has been demonstrated, using a“random graft polymerization” method to introduce a polymer onto theTiO₂ pigment surface through polymerizable or polymerizationinitiatinggroups attached to the surface of the particles. The major drawback ofthis approach is that polymers are formed in the presence of theparticles. It is more difficult to obtain well controlled systems wherethe unintended products can be cleaned up more easily.

Bi-state and/or tri-state electrophoretic display cells (or elements)having a three-dimensional architecture for compacting charged colorantparticles within the display cells are described in US PatentPublication 2010/0245981, published Sep. 30, 2010. A bi-state displaycell having a dark state and a clear state is provided by an electronicink with charged colorant particles in an optically transparent fluid. Aclear state is achieved when the colorant particles are compacted and acolored state is achieved when the colorant particles are spread. Anelectronic ink with charged white particles in a colored fluid enableswhite and spot-color states, with the color of the colored statedepending on the color of the fluid. The ink fluid is colored by a dye,nanoparticle colorants, pigments, or other suitable colorants. A whitestate is achieved when the white particles are spread and held inproximity to the surfaces closest to the viewer, and a colored state isachieved when the white particles are compacted to allow absorption bythe colorant fluid and subsequent reflection by a diffuse reflector inthe back of the cell, or when the white particles are distributedthroughout the colorant fluid to backscatter the light that has not beenabsorbed by the colorant fluid. By combining the white particles in thecolored fluid with a different colored resin on the back of the displaycell, a tri-state display cell is provided.

An electrophoretic display cell may include a three-dimensionalarchitecture to provide a clear optical state. In this architecture, thegeometrical shape of the display cell has narrowing portions in whichelectrophoretically/-electrokinetically translated colorant particlescollect and compact in response to appropriate bias conditions appliedto driving electrodes on opposite sides of the display cell. Thethree-dimensional structure of the display cell introduces additionalcontrol of electrophoretically/electrokinetically moving colorantparticles. As a result, desired functionalities can be achieved with amore stable electrophoretic/kinetic ink that resists irreversibleagglomeration of the particles, but maintains its ability to bothdisperse and collect and compact the particles. The driving electrodesare passivated with a dielectric layer, thus eliminating the possibilityof electrochemical interactions through the driving electrodes fromdirect contact with the electrophoretic ink. In other examples, thedriving electrodes are not passivated, thus allowing electrochemicalinteractions with the electrophoretic/kinetic ink.

An example of a stacked device architecture is shown in FIG. 1. Thisconfiguration allows stacking of colored layers forelectrophoretic/kinetic displays.

FIG. 1 illustrates a cross-sectional view of one example of stackedelectro-optical display 100. Electro-optical display 100 includes afirst display element 102 a, a second display element 102 b, and a thirddisplay element 102 c. Third display element 102 c is stacked on seconddisplay element 102 b, and second display element 102 b is stacked onfirst display element 102 a.

Each display unit includes a first substrate 104, a first electrode 106,a dielectric layer 108 including reservoir or recess regions 110, thinlayers 112, a display cell 114, a second electrode 116, and a secondsubstrate 118. Display cell 114 is filled with a carrier fluid 120 withcolorant particles 122. In some examples, thin layers 112 may be opaque.In other examples, thin layers 112 may be transparent.

First display element 102 a includes thin layers 112 a self-alignedwithin recess regions 110. First display element 102 a also includescolorant particles 122 a having a first color (e.g., cyan) for a fullcolor electro-optical display.

Second display element 102 b includes thin layers 112 b self-alignedwithin recess regions 110. Second display element 102 b also includescolorant particles 122 b having a second color (e.g., magenta) for afull color electro-optical display.

Third display element 102 c includes thin layers 112 c self-alignedwithin recess regions 110. Third display element 102 c also includescolorant particles 122 c having a third color (e.g., yellow) for a fullcolor electro-optical display. In other examples, colorant particles 122a, 122 b, and 122 c may include other suitable colors for providing anadditive or subtractive full color electro-optical display.

In the example illustrated in FIG. 1, in the electro-optical display100, first display element 102 a, second display element 102 b, andthird display element 102 c are aligned with each other. As such, thinlayers 112 a, 112 b, and 112 c are also aligned with each other. In thisexample, since recess regions 110 and self-aligned thin layers 112 a,112 b, and 112 c of each display element 102 a, 102 b, and 102 c,respectively, are aligned, the clear aperture for stackedelectro-optical display 100 is improved compared to a stackedelectro-optical display without such alignment.

In an alternate example (not shown), first display element 102 a, seconddisplay element 102 b, and third display element 102 c may be offsetfrom each other. As such, thin layers 112 a, 112 b, and 112 c are alsooffset from each other. In this example, since recess regions 110 andself-aligned thin layers 112 a, 112 b, and 112 c are just a fraction ofthe total area of each display element 102 a, 102 b, and 102 c,respectively, the clear aperture for stacked electro-optical display 100remains high regardless of the alignment between display elements 102 a,102 b, and 102 c. As such, the process for fabricating stackedelectro-optical display 100 is simplified. The self-aligned thin layers112 a, 112 b, and 112 c prevent tinting of each display element due tocolorant particles 122 a, 122 b, and 122 c, respectively, in the clearoptical state. Therefore, a stacked full color electro-optical displayhaving a bright, neutral white state and precise color control isprovided.

As indicated above, this architecture enables both clear and coloredstates. However, developing electronic inks that work in thisarchitecture has been challenging. The materials used inpresently-available commercial products do not work in thisarchitecture, since they do not provide clear states. Significantprogress toward developing working electronic inks for this architecturehas been made; see, e.g., PCT/US2009/060971 (“Electronic Inks”);PCT/US2009/060989 (“Dual Color Electronically Addressable Ink”); andPCT/US2009/060975 (“Electronic Inks”), all filed Oct. 16, 2009.

The foregoing discussion is directed primarily to stacked cells in anelectro-optical display. However, the functionalized pigments disclosedherein may also be employed in lateral cells in an electro-opticaldisplay.

FIG. 2 illustrates a cross-sectional view of one example of lateralelectro-optical display 200. Electro-optical display 200 includes adisplay element 202. Additional display elements may be disposedlaterally in the x and y directions, as side-by-side sub-pixels orsegments, with each display element containing inks 120+122 havingcolorant particles 122 of different colors, or having black colorantparticles that are collected to reveal patterned color filters orwavelength-selective reflectors below.

Each display element 202 is similar to electro-optical display 100 apreviously described and illustrated with reference to FIG. 1. Eachdisplay element 202 may include circular shaped thin layers 110 aself-aligned within recess regions 108. Each display element 202 mayalso include colorant particles 122 having a color (e.g., cyan, magenta,yellow, black, or white) for a full color electro-optical display. Inother examples, colorant particles 122 may include other suitable colorsfor providing an additive or subtractive full color electro-opticaldisplay.

In accordance with the teachings herein, new segment copolymer graftedpigment colorant particles via azide chemistry are provided for stableelectronic inks 120+122. This disclosure also discloses methods ofgrafting particles with segment copolymers via living polymerizationtechniques such as atom transfer radical polymerization (ATRP). Theparticles grafted with these novel functionalized segment copolymers canbe self-dispersed into non-polar solvents and supply both stericstabilization and particle charging functionality while minimizing theneed for additional surfactants. These functionalized segment copolymersare designed to have two portions that are grafted to the particle orsubsequent polymer ends in a step-wise fashion. The first portioncontains bulky organic groups to help facilitate the solubility of suchfunctionalized polymers in the solvent and provide a stericstabilization to the resulting particle dispersion. The second portioncontains either acidic or basic functionalized side groups thatfacilitate charging of the particle. Such stable and chargable/chargedparticle dispersions can be used for a variety of applications such aspigments as colorants in electrophoretic displays. This surfacemodification technology can be applied to both organic and inorganicpigments.

ATRP (Atom Transfer Radical Polymerization) is a surfaceinitiated livingpolymerization method, also referred to as living polymerization method,by which polymers can be formed. In this method, polymerization can onlyoccur on an initiator group, and is subsequently transferred to the endof the just added polymer chain. There are publications in thescientific literature about the application of this method to make newpolymers, but none of them deals with grafting functional segmentcopolymers onto a pigment surface.

In polymer chemistry, living polymerization is a form of additionpolymerization where the ability of a growing polymer chain to terminatehas been removed. This can be accomplished in a variety of ways. Chaintermination and chain transfer reactions are absent and the rate ofchain initiation is also much larger than the rate of chain propagation.The result is that the polymer chains grow at a more constant rate thanseen in traditional chain polymerization and their lengths remain verysimilar (i.e. they have a very low polydispersity index). Livingpolymerization is a popular method for synthesizing block copolymerssince the polymer can be synthesized in stages, each stage containing adifferent monomer. Additional advantages are predetermined molar massand control over end-groups.

In ATRP, the uniform polymer chain growth, which leads to lowpolydispersity, stems from use of a transition metal-based catalyst.This catalyst provides an equilibrium between active, and thereforepropagating, polymer and an inactive form of the polymer; known as thedormant form. Since the dormant state of the polymer is vastly preferredin this equilibrium, side reactions are suppressed. This equilibrium inturn lowers the concentration of propagating radicals, thereforesuppressing unintentional termination and controlling molecular weights.ATRP reactions are very robust in that they are tolerant of manyfunctional groups such as allyl, amino, epoxy, hydroxy, and vinyl groupspresent in either the monomer or the initiator. ATRP methods may also beadvantageous due to the ease of preparation, commercially available andinexpensive catalysts (copper complexes), pyridine based ligands andinitiators (alkyl halides).

In accordance with the teachings herein, a step-wise method of graftingnovel functionalized segment copolymers onto a particle or pigmentsurface via azide chemistry is provided, along with the formulation ofstable electronic inks based on such surface-modified pigments.

The process depicted herein employs a tetrafluorophenyl azide-basedinitiator. As shown in FIG. 3, the tetrafluorophenyl azide initiator maybe prepared by reacting commercially-available methylpentafluorobenzoate (1) with sodium azide to yield compound (2), inwhich the azide functionality substitutes in the para position.Hydrolysis of compound (2) with sodium hydroxide yieldstetrafluorophenyl azide acid (3). Reaction of tetrafluorophenyl azideacid (3) with thionyl chloride gives tetrafluorophenyl azide acidchloride (4), which in turn reacts with2-bromo-N-(3-hydroxypropyl)-2-methylpropanamide (5) to givetetrafluorophenyl azide-based initiator (6). The azide-based initiatormay be used to form the tri-block (or di-block) copolymers, as describedin greater detail below.

Examples of structures of segment copolymers with different segments areshown in Scheme 1 as segment copolymers 1, 2 and 3, each with slightlydifferent segment chains.

wherein,

L₁, L₂, and L₃ are a covalent bond or chemical structure providing acovalent bond between different segments, such as C—C, C═C, C═N, C≡C, orN≡N, for example.

SG₁ and SG₂ each independently represent a solublizing oligomer orsolubilizing sterically bulky group, which helps to improve thesolubility of the polymer and stabilize the colorant particles; they maybe any oligomers of olefin, (meth)acrylates, styrenes, oxides, ethers,or esters or sterically bulky group such as alkyl groups, alkoxy groups,branched alkyl groups, branched alkoxy groups, aliphatic esters,branched aliphatic esters, and substituted phenyl groups.

FG represents an oligomer or functional group that provides chargingsites/charges to pigment surfaces; it can be an oligomer or monomericmoiety that contains acidic or basic functional groups, wherein examplesof acidic functional groups include hydroxyl, carboxylate, a sulfonicacid, a phosphonic acid, a phosphorous acid, and the like, and whereinexamples of basic functional groups include primary amine, secondaryamine, tertiary amine, pyridine, imidazoline, and the like. Specificexamples include oligomers or monomers of (meth)acrylic acid,2-sulfoethyl methacylate, dimethylamino ethyl(meth)acrylate, anddiethylamino ethyl styrene.

The letters x, y and z are each independently an integer between 1 andabout 5,000.

The letter n represents an integer between 2 and about 100.

Scheme 2 shows general examples of segment copolymers 4, 5, and 6 thatcan be grafted onto pigment surfaces, in which different segments areconnected with carbon-carbon single bond (L=C—C).

wherein,

SG₁ and SG₂, FG, x, y, and z, and n are as described for Scheme 1.

Scheme 3 shows a few examples of vinyl-containing small moleculemonomers that can be grafted onto pigment surfaces to providestabilizing functions.

wherein,

R₁, R₂, R₃, R₄ and R₅ are each independently selected from the groupconsisting of C1-C30 alkyl, C1-C30 alkenyl, C1-C30 alkynyl, C1-C30 aryl,C1-C30 alkoxy, C1-C30 phenoxy, C1-C30 thioalkyl, C1-C30 thioaryl,C(O)OR₆, N(R₇)(R₈), C(O)N(R₉)(R₁₀), F, Cl, Br, NO₂, CN, acyl,carboxylate and hydroxy, wherein R₆, R₇, R₈, R₉ and R₁₀ are eachindependently selected from the group consisting of hydrogen, C1-C30alkyl and C1-C30 aryl, and so forth. R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈ andR₉ may or may not be identical.

Scheme 3A shows a few more specific examples that can be used for makingSG₁ or SG₂, in which these monomers are oligomeric monomers.

wherein,

m=1 to about 5,000.

The examples shown in Scheme 3A are surfactant molecules, and may bereferred to as macromolecule monomers. As used herein, macromoleculemonomers refer to oligomers or polymers that have polymerizable groups,such as styrene, acrylate, or methacrylate moieties.

Scheme 4 shows some examples of monomers that can be grafted ontopigment surfaces to provide charges to the pigment surfaces.

wherein,

R₁, R₂, R₃, R₄ and R₅ are each independently selected from the groupconsisting of C1-C30 alkyl, C1-C30 alkenyl, C1-C30 alkynyl, C1-C30 aryl,C1-C30 alkoxy, C1-C30 phenoxy, C1-C30 thioalkyl, C1-C30 thioaryl,C(O)OR₆, N(R₇)(R₈), C(O)N(R₉)(R₁₀), F, Cl, Br, NO₂, CN, acyl,carboxylate and hydroxy, wherein R₆, R₇, R₈, R₉ and R₁₀ are eachindependently selected from the group consisting of hydrogen, C1-C30alkyl and C1-C30 aryl, and so forth. R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈ andR₉ may or may not be identical.

Scheme 5 describes a method of grafting such functionalized segmentcopolymer onto pigment surfaces via azide chemistry. Tetrafluorophenylazide initiator I initiates the polymerization of the first segmentmonomer to give the first segment tetrafluorophenyl azide living polymerII. Addition of second monomer to the living polymer II yieldtwo-segment tetrafluorophenyl living polymer III. Addition of thirdmonomer to living polymer III give three-segment tetrafluorophenyl azidepolymer IV. By repeating steps 1, 2 and 3 n times, the final segmentcopolymer V can be formed. It is noteworthy that one can change theorder of reaction steps for living polymerization when repeating steps1, 2 and 3 to form different segment copolymers V. Coupling reaction ofinorganic or organic pigments with tetrafluorophenyl azide polymer Vupon UV or thermal irradiation gives functionalized segment copolymersgrafted pigment VI. Such segment copolymers grafted pigments can bemixed with other dispersants or charge directors to form charged andstable pigment dispersions for electronic ink applications.

wherein,

SG₁ and SG₂ each independently represent a solublizing oligomer orsolubilizing sterically bulky group, which helps to improve thesolubility of the polymer and stabilize the colorant particles; they maybe any oligomers of olefin, (meth)acrylates, styrenes, oxides, ethers,or esters or sterically bulky group such as alkyl groups, alkoxy groups,branched alkyl groups, branched alkoxy groups, aliphatic esters,branched aliphatic esters, and substituted phenyl groups.

FG represents an oligomer or functional group that provides chargingsites/charges to pigment surfaces; it can be an oligomer or monomericmoiety that contains acidic or basic functional groups, wherein examplesof acidic functional groups include hydroxyl, carboxylate, a sulfonicacid, a phosphonic acid, a phosphorous acid, and the like, and whereinexamples of basic functional groups include primary amine, secondaryamine, tertiary amine, pyridine, imidazoline, and the like. Specificexamples include oligomers or monomers of (meth)acrylic acid,2-sulfoethyl methacylate, dimethylamino ethyl(meth)acrylate, anddiethylamino ethyl styrene.

The letters x, y and z are an integer between 1 and about 5,000.

The letter n represents an integer between 2 and about 100.

The sphere ball represents any possible electrophoretic particles withall possible colors such as RGB or CYMK. It may be a colored pigment,colored polymeric particles with the sizes ranging from 50 nm to 1 μm.It may be organic or inorganic.

Scheme 6 describes a specific example of such segment copolymers graftedpigments that bear negative charges via azide chemisrty. This exampledescribes polyacrylic acid and polystyrene based segment copolymers.Tetrafluorophenyl azide initiator I undergoes the first steppolymerization with the first segment monomer, for example, substitutedstyrene, to give the first segment, namely, a polystyrenetetrafluorophenyl azide living polymer II. Living polymer II undergoes asecond step polymerization with the second segment monomer, for example,acrylic acid, to give the two-segment living polymer III, namely, apolystyrene and polyacrylic acid tetrafluorophenyl living polymer III.Living polymer III undergoes a third step polymerization with the thirdsegment monomer, for example, substituted styrene, to give thethree-segment living polymer IV, namely, a polystyrene, polyacrylic acidand polystyrene tetrafluorophenyl azide polymer IV. By repeating steps1, 2 and 3 n times, the final segment copolymer V can be formed. It isnoteworthy that one can change the order of reaction steps for livingpolymerization when repeating steps 1, 2 and 3 to form different segmentcopolymers V. Coupling reaction of inorganic or organic pigments withthe three-segment (polystyrene, polyacrylic acid and polystyrene)tetrafluorophenyl azide polymer V upon UV irradiation givesfunctionalized segment copolymer grafted pigment VI. Such segmentcopolymers grafted pigments can be mixed with other dispersants orcharge directors to form negatively charged and stable pigmentdispersions for electronic ink applications.

wherein,

R represents sterically bulky group, which helps to improve thesolubility of the polymer and stabilize the nano-composite material. Itcould be any alkyl groups, alkoxy groups, branched alkyl groups andbranched alkoxy groups.

The letters x, y and z are an integer between 1 and about 5,000.

The letter n represents an integer between 2 and about 100.

The sphere ball represents any possible electrophoretic particles withall possible colors such as RGB or CYMK. It can be colored pigments,colored polymeric particles with the sizes ranging from 50 nm to 1 μm.

Scheme 7 describes a specific example of such tri-segment copolymersgrafted pigments that should bear positive charges. It describespolyacrylate ammonium salts and polystyrene based tri-segmentcopolymers. Tetrafluorophenyl azide initiator I undergoes the first steppolymerization with the first segment monomer, for example, substitutedstyrenes, to give the first block, namely, a polystyrenetetrafluorophenyl azide living polymer II. Living polymer II undergoes asecond step polymerization with the second segment monomer, for example,acrylate ammonium salts, to give a two-segment living polymer III,namely, a polystyrene and polyacrylate ammonium salts tetrafluorophenylliving polymer III. Living polymer III undergoes a third steppolymerization with the third segment monomer, for example, substitutedstyrene, to give the three-segment living polymer IV, namely, apolystyrene, polyacrylate ammonium salts and polystyrenetetrafluorophenyl azide polymer IV. By repeating steps 1, 2 and 3 ntimes, the final segment copolymer V can be formed. It is noteworthythat one can change the order of reaction steps for livingpolymerization when repeating steps 1, 2 and 3 to form different segmentcopolymers V. Coupling reaction of inorganic or organic pigments withthree-segment polystyrene, polyacrylic acid ammonium salts andpolystyrene tetrafluorophenyl azide polymer V upon UV irradiation givesfunctionalized segment copolymers grafted pigment VI. Such segmentcopolymers grafted pigments can be mixed with other dispersants orcharge directors to form charged and stable pigment dispersions forelectronic ink applications.

wherein,

R₁, R₂, R₃, R₄ and R₅ are each independently selected from the groupconsisting of C1-C30 alkyl, C1-C30 alkenyl, C1-C30 alkynyl, C1-C30 aryl,C1-C30 alkoxy, C1-C30 phenoxy, C1-C30 thioalkyl, C1-C30 thioaryl,C(O)OR₆, N(R₇)(R₈), C(O)N(R₉)(R₁₀), F, Cl, Br, NO₂, CN, acyl,carboxylate and hydroxy, wherein R₆, R₇, R₈, R₉ and R₁₀ are eachindependently selected from the group consisting of hydrogen, C1-C30alkyl and C1-C30 aryl, and so forth. The residues R₁, R₂, R₃, R₄, R₅,R₆, R₇, R₈ and R₉ may or may not be identical.

The letters x, y and z are an integer between 1 and about 5,000.

The letter n represents an integer between 2 and about 100.

The sphere ball represents any possible electrophoretic particles withall possible colors such as RGB or CYMK. It can be a colored pigment ora colored polymeric particle, with a particle size ranging from about 50nm to 1 μm. It may be organic or inorganic.

An example process 400 for making the nitrogen-linked surfacefunction-alized pigment particle is illustrated in FIG. 4. The process400 includes providing 402 an azide. The process 400 further includescausing 404 the azide to initiate polymerization of a first blockmonomer to give a first block azide living polymer. The process 400additionally includes adding 406 a second monomer to the first blockliving polymer to give a two-block azide living copolymer and form afirst segment. The process 400 also includes forming 408 at least oneadditional segment by adding, in any order, a first block monomer and asecond block monomer to form a two-block living segment copolymer. Theprocess 400 further includes causing 410 an inorganic or organic pigmentparticle to undergo a coupling reaction with the azide on the two-blockliving segment copolymer to form a functionalized di-block segmentcopolymer coupled to the pigment particle through a nitrogen link.

The example process in the previous paragraph forms a di-block segmentcopolymer. To form a tri-block segment copolymer, the process may becontinued by adding a third monomer to the two-block living azidepolymer, which yields a three-block azide living segment copolymer. Inthe forming step above, at least one additional segment is formed byadding, in any order, a first block monomer, a second block monomer, anda third block monomer to form a tri-block living segment copolymer.Finally, the inorganic or organic pigment particle is caused to undergoa coupling reaction with the azide on the three-block living segmentcopolymer to form a functionalized tri-block segment copolymer coupledonto the pigment particle through a nitrogen link.

Turning now to electronic inks 120+122 that employ the functionalizedpigments 122 discussed above, examples of such electronic inks generallyinclude a non-polar carrier fluid 120 (i.e., a fluid having a lowdielectric constant k such as, e.g., less than about 20, or, in somecases, less than about 2). Such fluids tend to reduce leakages ofelectric current when driving the display, as well as increase theelectric field present in the fluid. As used herein, the “carrier fluid”is a fluid or medium that fills up a viewing area defined in anelectronic ink display and is generally configured as a vehicle to carrycolorant particles therein. In response to a sufficient electricpotential or field applied to the colorant particles 122 while drivingelectrodes of the display, the colorant particles tend to move and/orrotate to various spots within the viewing area in order to produce adesired visible effect in the display cell to display an image. Thenonpolar carrier fluid 120 includes, for example, one or more non-polarcarrier fluids selected from hydrocarbons, halogenated or partiallyhalogenated hydrocarbons, and/or siloxanes. Some specific examples ofnon-polar carrier fluids include perchloroethylene, cyclohexane,dodecane, mineral oil, isoparaffinic fluids, cyclopentasiloxane,cyclohexasiloxane, octamethylcyclosiloxane, and combinations thereof.

The colorant particles 122 are dispersed in the carrier fluid. As usedherein, the term “colorant particles” refers to particles that produce acolor. Some non-limiting examples of suitable colorant particles 122include the surface-modified pigment particles described above, whichmay be dispersible in the non-polar carrier fluid 120 due to thepresence of the di-block or tri-block segment copolymers attached to thepigment surface. However, the total elimination of dispersants, such asthose commonly used in dispersing pigment particles in the non-polarcarrier fluid, may not be attained. In that case, the electronic ink120+122 may include one or more suitable dispersants. Such dispersantsinclude hyperdispersants such as those of the SOLSPERSE® seriesmanufactured by Lubrizol Corp., Wickliffe, Ohio (e.g., SOLSPERSE® 3000,SOLSPERSE® 8000, SOLSPERSE® 9000, SOLSPERSE® 11200, SOLSPERSE® 13840,SOLSPERSE® 16000, SOLSPERSE® 17000, SOLSPERSE® 18000, SOLSPERSE® 19000,SOLSPERSE® 21000, and SOLSPERSE® 27000); various dispersantsmanufactured by BYK-chemie, Gmbh, Germany, (e.g., DISPERBYK® 110,DISPERBYK® 163, DISPERBYK® 170, and DISPERBYK® 180); various dispersantsmanufactured by Evonik Goldschmidt GMBH LLC, Germany, (e.g., TEGO® 630,TEGO® 650, TEGO® 651, TEGO® 655, TEGO® 685, and TEGO® 1000); and variousdispersants manufactured by Sigma-Aldrich, St. Louis, Mo., (e.g., SPAN®20, SPAN® 60, SPAN® 80, and SPAN® 85).

In some examples, the concentration of pigment 122 in the electronic ink120+122 ranges from about 0.01 to 20 percent by weight (wt %). In otherexamples, the concentration of the pigment ranges from about 1 to 10 wt%. In some examples, the concentration of dispersant in the electronicink ranges from about 0.5 to 20 percent by weight (wt %). In otherexamples, the concentration of the dispersant ranges from about 1 to 10wt %. The carrier fluid 120 makes up the balance of the ink.

There is commonly a charge director employed in electronic inks. As usedherein, the term “charge director” refers to a material that, when used,facilitates charging of the colorant particles. In an example, thecharge director is basic and reacts with the acid-modified colorantparticle to negatively charge the particle. In other words, the chargingof the particle is accomplished via an acid-base reaction between thecharge director and the acid-modified particle surface. It is to beunderstood that the charge director may also be used in the electronicink to prevent undesirable aggregation of the colorant in the carrierfluid. In other cases, the charge director is acidic and reacts with thebase-modified colorant particle to positively charge the particle.Again, the charging of the particle is accomplished via an acid-basereaction between the charge director and the base-modified particlesurface or adsorption of charged micelles.

The charge director may be selected from small molecules or polymersthat are capable of forming reverse micelles in the non-polar carrierfluid. Such charge directors are generally colorless and tend to bedispersible or soluble in the carrier fluid.

In a non-limiting example, the charge director is selected from aneutral and non-dissociable monomer or polymer such as, e.g., apolyisobutylene succinimide amine, which has a molecular structure asfollows:

where n is selected from a whole number ranging from 15 to 100.

Another example of the charge director includes an ionizable moleculethat is capable of disassociating to form charges. Non-limiting examplesof such charge directors include sodium di-2-ethylhexylsulfosuccinateand dioctyl sulfosuccinate. The molecular structure of dioctylsulfosuccinate is as follows:

Yet another example of the charge director includes a zwitterion chargedirector such as, e.g., lecithin. The molecular structure of lecithin isas shown as follows:

The foregoing discussion has been directed to the functionalization ofTiO₂ pigment particles (white color). However, the teachings herein areequally applicable to other pigments, whether inorganic or organic, andof whatever color. Such inorganic and organic pigments are describedfurther below, along with examples of different colors.

The pigment particles are selected from organic or inorganic pigments,and have an average particle size ranging from about 1 nm to about 10μm. In some examples, the average particle size ranges from about 10 nmto about 1 μm. In other examples, the average particle size ranges fromabout 30 to 500 nm. In still other examples, the average particle sizeranges from about 50 nm to 1 μm. Such organic or inorganic pigmentparticles may be selected from black pigment particles, yellow pigmentparticles, magenta pigment particles, red pigment particles, violetpigments, cyan pigment particles, blue pigment particles, green pigmentparticles, orange pigment particles, brown pigment particles, and whitepigment particles. In some instances, the organic or inorganic pigmentparticles may include spot-color pigment particles, which are formedfrom a combination of a predefined ratio of two or more primary colorpigment particles. To the extent that the generic pigments on theforegoing list can be functionalized as taught herein, such pigments maybe used in the practice of the teachings herein. Likewise, to the extentthat the following examples of specific pigments can be functionalizedas taught herein, such pigments may be used in the practice of theteachings herein.

A non-limiting example of a suitable inorganic black pigment includescarbon black. Examples of carbon black pigments include thosemanufactured by Mitsubishi Chemical Corporation, Japan (such as, e.g.,carbon black No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52,MA7, MA8, MA100, and No. 2200B); various carbon black pigments of theRAVEN® series manufactured by Columbian Chemicals Company, Marietta,Ga., (such as, e.g., RAVEN® 5750, RAVEN® 5250, RAVEN® 5000, RAVEN® 3500,RAVEN® 1255, and RAVEN® 700); various carbon black pigments of theREGAL® series, the MOGUL® series, or the MONARCH® series manufactured byCabot Corporation, Boston, Mass., (such as, e.g., REGAL® 400R, REGAL®330R, REGAL® 660R, MOGUL® L, MONARCH® 700, MONARCH® 800, MONARCH® 880,MONARCH® 900, MONARCH® 1000, MONARCH® 1100, MONARCH® 1300, and MONARCH®1400); and various black pigments manufactured by Evonik DegussaCorporation, Parsippany, N.J., (such as, e.g., Color Black FW1, ColorBlack FW2, Color Black FW2V, Color Black FW18, Color Black FW200, ColorBlack S150, Color Black S160, Color Black S170, PRINTEX® 35, PRINTEX® U,PRINTEX® V, PRINTEX® 140U, Special Black 5, Special Black 4A, andSpecial Black 4). A non-limiting example of an organic black pigmentincludes aniline black, such as C.I. Pigment Black 1.

Other examples of inorganic pigments include metal oxides and ceramics,such as the oxides of iron, zinc, cobalt, manganese, nickel.Non-limiting examples of suitable inorganic pigments include those fromthe Shepherd Color Company (Cincinnati, Ohio) such as Black 10C909A,Black 10P922, Black 1 G, Black 20F944, Black 30C933, Black 30C940, Black30C965, Black 376A, Black 40P925, Black 411A, Black 430, Black 444, Blue10F545, Blue 10G511, Blue 10G551, Blue 10K525, Blue 10K579, Blue 211,Blue 212, Blue 214, Blue 300527, Blue 300588, Blue 300591, Blue 385,Blue 40P585, Blue 424, Brown 100873, Brown 10P835, Brown 10P850, Brown10P857, Brown 157, Brown 200819, Green 10K637, Green 187 B, Green 223,Green 260, Green 300612, Green 300654, Green 300678, Green 40P601, Green410, Orange 10P320, StarLight FL 37, StarLight FL105, StarLight FL500,Violet 11, Violet 11C, Violet 92, Yellow 10C112, Yellow 10C242, Yellow10C272, Yellow 10P110, Yellow 10P225, Yellow 10P270, Yellow 196, Yellow20P296, Yellow 30C119, Yellow 30C236, Yellow 40P140, Yellow 40P280.

In addition to the foregoing inorganic pigments, the same teachings maybe employed with organic pigments. The following is a list of organicpigments that may be treated in accordance with the teachings herein.

Non-limiting examples of suitable yellow pigments include C.I. PigmentYellow 1, C.I. Pigment Yellow 2, C.I. Pigment Yellow 3, C.I. PigmentYellow 4, C.I. Pigment Yellow 5, C.I. Pigment Yellow 6, C.I. PigmentYellow 7, C.I. Pigment Yellow 10, C.I. Pigment Yellow 11, C.I. PigmentYellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. PigmentYellow 16, C.I. Pigment Yellow 17, C.I. Pigment Yellow 24, C.I. PigmentYellow 34, C.I. Pigment Yellow 35, C.I. Pigment Yellow 37, C.I. PigmentYellow 53, C.I. Pigment Yellow 55, C.I. Pigment Yellow 65, C.I. PigmentYellow 73, C.I. Pigment Yellow 74, C.I. Pigment Yellow 75, C.I. PigmentYellow 81, C.I. Pigment Yellow 83, C.I. Pigment Yellow 93, C.I. PigmentYellow 94, C.I. Pigment Yellow 95, C.I. Pigment Yellow 97, C.I. PigmentYellow 98, C.I. Pigment Yellow 99, C.I. Pigment Yellow 108, C.I. PigmentYellow 109, C.I. Pigment Yellow 110, C.I. Pigment Yellow 113, C.I.Pigment Yellow 114, C.I. Pigment Yellow 117, C.I. Pigment Yellow 120,C.I. Pigment Yellow 124, C.I. Pigment Yellow 128, C.I. Pigment Yellow129, C.I. Pigment Yellow 133, C.I. Pigment Yellow 138, C.I. PigmentYellow 139, C.I. Pigment Yellow 147, C.I. Pigment Yellow 151, C.I.Pigment Yellow 153, C.I. Pigment Yellow 154, Pigment Yellow 155, C.I.Pigment Yellow 167, C.I. Pigment Yellow 172, and C.I. Pigment Yellow180.

Non-limiting examples of suitable magenta or red or violet organicpigments include C.I. Pigment Red 1, C.I. Pigment Red 2, C.I. PigmentRed 3, C.I. Pigment Red 4, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I.Pigment Red 7, C.I. Pigment Red 8, C.I. Pigment Red 9, C.I. Pigment Red10, C.I. Pigment Red 11, C.I. Pigment Red 12, C.I. Pigment Red 14, C.I.Pigment Red 15, C.I. Pigment Red 16, C.I. Pigment Red 17, C.I. PigmentRed 18, C.I. Pigment Red 19, C.I. Pigment Red 21, C.I. Pigment Red 22,C.I. Pigment Red 23, C.I. Pigment Red 30, C.I. Pigment Red 31, C.I.Pigment Red 32, C.I. Pigment Red 37, C.I. Pigment Red 38, C.I. PigmentRed 40, C.I. Pigment Red 41, C.I. Pigment Red 42, C.I. Pigment Red48(Ca), C.I. Pigment Red 48(Mn), C.I. Pigment Red 57(Ca), C.I. PigmentRed 57:1, C.I. Pigment Red 88, C.I. Pigment Red 112, C.I. Pigment Red114, C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 144,C.I. Pigment Red 146, C.I. Pigment Red 149, C.I. Pigment Red 150, C.I.Pigment Red 166, C.I. Pigment Red 168, C.I. Pigment Red 170, C.I.Pigment Red 171, C.I. Pigment Red 175, C.I. Pigment Red 176, C.I.Pigment Red 177, C.I. Pigment Red 178, C.I. Pigment Red 179, C.I.Pigment Red 184, C.I. Pigment Red 185, C.I. Pigment Red 187, C.I.Pigment Red 202, C.I. Pigment Red 209, C.I. Pigment Red 219, C.I.Pigment Red 224, C.I. Pigment Red 245, C.I. Pigment Violet 19, C.I.Pigment Violet 23, C.I. Pigment Violet 32, C.I. Pigment Violet 33, C.I.Pigment Violet 36, C.I. Pigment Violet 38, C.I. Pigment Violet 43, andC.I. Pigment Violet 50.

Non-limiting examples of blue or cyan organic pigments include C.I.Pigment Blue 1, C.I. Pigment Blue 2, C.I. Pigment Blue 3, C.I. PigmentBlue 15, C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:34, C.I. PigmentBlue 15:4, C.I. Pigment Blue 16, C.I. Pigment Blue 18, C.I. Pigment Blue22, C.I. Pigment Blue 25, C.I. Pigment Blue 60, C.I. Pigment Blue 65,C.I. Pigment Blue 66, C.I. Vat Blue 4, and C.I. Vat Blue 60.

Non-limiting examples of green organic pigments include C.I. PigmentGreen 1, C.I. Pigment Green2, C.I. Pigment Green, 4, C.I. Pigment Green7, C.I. Pigment Green 8, C.I. Pigment Green 10, C.I. Pigment Green 36,and C.I. Pigment Green 45.

Non-limiting examples of brown organic pigments include C.I. PigmentBrown 1, C.I. Pigment Brown 5, C.I. Pigment Brown 22, C.I. Pigment Brown23, C.I. Pigment Brown 25, and C.I. Pigment Brown, C.I. Pigment Brown41, and C.I. Pigment Brown 42.

Non-limiting examples of orange organic pigments include C.I. PigmentOrange 1, C.I. Pigment Orange 2, C.I. Pigment Orange 5, C.I. PigmentOrange 7, C.I. Pigment Orange 13, C.I. Pigment Orange 15, C.I. PigmentOrange 16, C.I. Pigment Orange 17, C.I. Pigment Orange 19, C.I. PigmentOrange 24, C.I. Pigment Orange 34, C.I. Pigment Orange 36, C.I. PigmentOrange 38, C.I. Pigment Orange 40, C.I. Pigment Orange 43, and C.I.Pigment Orange 66.

Advantageously, the herein-disclosed methods of grafting particles withnovel functionalized segment copolymers and their dispersion innon-polar solvents results in minimal need for additional surfactants orcharge directors. The methods use a step-wise process to two or threedifferent chemically-functionalized segment polymers which areconsecutively grafted onto the particle/polymer surface. Each block ofthese functionalized segment copolymers can be designed to optimize itsintended function in the system based on the specific particlechemistry, solvent choice, and system requirement. For example, for thetri-block segment copolymer, the inner block can be designed to providethe best compatibility to the particle surface chemistry whileexhibiting adequate solubility in the non-polar solvent. The middleblock can be designed to achieve the appropriate charge functionality incombination with the particle chemistry and other additives. The outerblock can be designed to provide adequate steric stabilization toprevent agglomeration based on system requirements. For example, theouter block could be different for the same particle species in a singlespecies ink compared to a dual species/charge system. Using this newtechnology, one can also make stable dual color electronic inks based onboth positively charged particles and negatively charged particles,since the charges are separated by steric stabilizing groups, whichprevents the agglomeration and precipitation of the two particle speciesdue to the attraction of opposite charges.

The electronic inks based on such segment copolymers grafted ontopigment particles are very stable, since the both the chargeproducingand steric stabilization groups are covalently bonded to the pigmentsurface. This approach contributes to the robustness of the particle.Because there is minimal need to add additional surfactants to stabilizethe ink, the final electronic ink will have low background charge, andas a result will exhibit less field screening effects which limit theclearing performance of electronic inks. This surface modificationtechnology can be applied to both organic and inorganic pigments.

The foregoing functionalized pigments have been described with specificapplication to electronic inks. However, the functionalized pigments mayfind use in other ink technologies that employ non-aqueous inks. Anexample of such other ink technology is liquid electrophoretic ink (LEP)used in commercial digital printers.

What is claimed is:
 1. Pigment based inks including: a non-polar carrier fluid; and a surface-functionalized pigment particle including a nitrogen-linked moiety to the surface of the pigment particle through a nitrogen link at one end of the nitrogen-linked moiety and a segment copolymer having at least two blocks attached at another end, the pigment particle suspended in the nonpolar carrier fluid.
 2. The inks of claim 1 wherein the non-polar carrier fluid is a non-polar solvent selected from the group consisting of hydrocarbons, halogenated hydrocarbons, partially halogenated hydrocarbons, and siloxanes.
 3. The inks of claim 1 wherein the pigment particle is selected from the group consisting of black pigment particles, yellow pigment particles, magenta pigment particles, red pigment particles, violet pigment particles, cyan pigment particles, blue pigment particles, green pigment particles, orange pigment particles, brown pigment particles, and white pigment particles.
 4. The inks of claim 1 wherein the segment copolymer has a formula selected from the group consisting of segment copolymer 1, segment copolymer 2, and segment copolymer 3, as shown below:

wherein, L₁, L₂, and L₃ are each independently a covalent bond or chemical structure providing a covalent bond between different blocks selected from the group consisting of C—C, C═C, C═N, C≡C, and N≡N; SG₁ and SG₂ each independently represent a solublizing and sterically bulky group, which helps to improve the solubility of the polymer and stabilize the colorant particles, selected from the group consisting of alkyl groups, alkoxy groups, branched alkyl groups, branched alkoxy groups, aliphatic esters, branched aliphatic esters, substituted phenyl groups, and macromolecular monomers; FG represents a functional group that provides charging sites to pigment surfaces, selected from acidic functional groups and basic groups; x, y and z are each independently an integer between 1 and about 5,000; and n is an integer between 2 and about
 100. 5. The inks of claim 4 wherein FG is selected from the group consisting of primary amines, secondary amines, tertiary amines, amides, nitriles, isonitriles, cyanates, isocyanates, thiocyanates, isothiocyanates, azides, thiols, thiolates, sulfides, sulfinates, sulfonates, phosphates, hydroxyls, alcoholates, phenolates, carbonyls, carboxylates, phosphines, phosphine oxides, phosphonic acids, phosphoramides, and phosphates.
 6. The inks of claim 4 wherein at least one of SG₁ and SG₂ comprise the macromolecule monomer selected from the group consisting of

wherein m is an integer from 1 to 5,000.
 7. The inks of claim 4 wherein one or both of SG₁ and SG₂ comprises

wherein, R₁, R₂, R₃, R₄ and R₅ are each independently selected from the group consisting of C1-C30 alkyl, C1-C30 alkenyl, C1-C30 alkynyl, ClC30 aryl, C1-C30 alkoxy, C1-C30 phenoxy, C1-C30 thioalkyl, C1-C30 thioaryl, C(O)OR₆, N(R₇)(R₈), C(O)N(R₉)(R₁₀), F, Cl, Br, NO₂, CN, acyl, carboxylate and hydroxy, wherein R₆, R₇, R₈, R₉ and R₁₀ are each independently selected from the group consisting of hydrogen, C1-C30 alkyl and C1-C30 aryl, and wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈ and R₉ may or may not be identical.
 8. The inks of claim 1 further including a charge director, wherein the charge director is a small molecule or polymer that is capable of forming reverse micelles in the non-polar carrier fluid.
 9. In combination, an electronic display and an electronic ink, wherein the electronic display includes: a first electrode; a second electrode; and a display cell having a recess defined by a dielectric material, the first electrode, and the second electrode, the display cell containing the electronic ink; and wherein the electronic ink includes: a non-polar carrier fluid; and a surface-functionalized pigment particle including a nitrogen-linked moiety to the surface of the pigment particle through a nitrogen link at one end of the nitrogen-linked moiety and a segment copolymer having at least two blocks attached at another end, the pigment particle suspended in the non-polar carrier fluid.
 10. The combination of claim 9 wherein the electronic display includes a plurality of display cells in a stacked configuration, associated first electrodes and second electrodes, and a plurality of electronic inks of different colors, each display cell containing an electronic ink of a different color.
 11. The combination of claim 9 wherein the non-polar carrier fluid is a non-polar solvent selected from the group consisting of hydrocarbons, halogenated hydrocarbons, partially halogenated hydrocarbons, and siloxanes.
 12. The combination of claim 9 wherein the colored pigment is a colored particle having a size ranging from 1 nm to 10 μm and is selected from the group consisting of black pigment particles, yellow pigment particles, magenta pigment particles, red pigment particles, violet pigment particles, cyan pigment particles, blue pigment particles, green pigment particles, orange pigment particles, brown pigment particles, and white pigment particles.
 13. The combination of claim 9 further including a charge director, wherein the charge director is a small molecule or polymer that is capable of forming reverse micelles in the non-polar carrier fluid.
 14. A method for making a nitrogen-linked surface functionalized pigment particle including: providing an azide; causing the azide to initiate polymerization of a first block monomer to give a first block azide living polymer; adding a second monomer to the first block living polymer to give a two-block azide living copolymer and form a first segment; forming at least one additional segment by adding, in any order, a first block monomer and a second block monomer to form a two-block living segment copolymer; and causing an inorganic or organic pigment particle to undergo a coupling reaction with the azide on the two-block living segment copolymer to form a functionalized di-block segment copolymer coupled to the pigment particle through a nitrogen link.
 15. The method of claim 14 further comprising: after the adding step, adding a third monomer to the two-block azide living block copolymer, which yields a three-block azide living copolymer, in the forming step, forming at least one additional segment by adding, in any order, a first block monomer, a second block monomer, and a third block monomer to form a tri-block living segment copolymer; and causing the inorganic or organic pigment particle to undergo a coupling reaction with the azide on the three-block living segment copolymer to form a functionalized tri-block segment copolymer coupled onto the pigment particle through a nitrogen link. 